In the oil and gas industry, bores are drilled to access subsurface hydrocarbon-bearing formations. The bores are drilled using bits forming parts of bottom hole assemblies (BHAs) mounted on the ends of strings of drill pipe. A drill pipe string comprises a number of drill pipe lengths, which can be stored on surface as “stands”. Each stand may comprise three or four lengths of drill pipe. As a drill string is advanced into a bore, new stands of pipe are added to the upper end of the string. As a bore advances, casing and/or completion tubing can be run into the bore in order to, for example, stabilise the bore. Casing, completion tubing, drill pipes, liners, and the like, are herein collectively referred to as “tubulars”.
The drilled bore is typically filled with drilling fluid, mud or brine. Thus, as tubulars are lowered into the bore, the drilling fluid surrounds the tubular. Some tubulars are configured such that this drilling fluid may flow into the hollow tubular as it passes into the fluid-filled bore (so-called “self-filling” tubulars). However, in other circumstances the tubular is not self-filling and must be top-filled. For example, when the tubular is provided with a float, or non-return value. In the absence of fluid in the tubular, the external hydrostatic pressure may reach a level sufficient to crush or collapse the hollow tubular.
Conventionally, such tubulars will be top-filled by trickling drilling fluid into their open upper end. This top-filling operation is tricky and potentially messy, with spillage of drilling fluid being common. Also, top-filling tubulars can take a significant amount of time and it will often be required to clean-up any spills, particularly in the case of drill strings, as drill pipe ends often have a region of restricted cross-section. Furthermore, it has been identified that when contaminants or debris in top filling fluid are allowed to enter the tubulars, it can cause serious problems with subsequent operations, such as inhibiting mating of sealing faces of sections of completion tubings, etc. Accordingly, some operators require that top filling fluid is filtered as the fluid is trickled into the tubulars, which tends to create further delays.
PCT/GB2007/002172 (Churchill) discusses apparatus for top filling and is incorporated herein by reference.